CN1310641A - Vinyl acetate catalyst comprising metallic palladium and gold, and cupric acetate - Google Patents

Abstract

A catalyst for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium and gold, and cupric acetate. Use of this catalyst results in a reaction having a relatively low selectivity to carbon dioxide.

Description

Vinyl Acetate Catalysts Containing Metallic Palladium and Gold and Copper Acetate

Background of the Invention

scope of invention

This invention relates to new and improved catalysts for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid.

Background information including relevant technical notes

It is known to produce vinyl acetate by the reaction of ethylene, oxygen and acetic acid using a catalyst composed of metallic palladium and gold supported on a support. While processes using such catalysts can produce vinyl acetate at high levels of productivity, such levels of productivity are limited by the formation of undesirable by-products, especially carbon dioxide. The formation of any product or by-product may be expressed as a percent selectivity, specified as the amount of such product that can be expressed as a percentage of the theoretical maximum formed by the reactants. Therefore, any method of reducing CO2 production (as indicated by a lower CO2 percent selectivity) is highly desirable.

The following references may be considered as material for the invention claimed herein.

US3775342 issued to Kronig et al. on November 27, 1973 and US3822308 issued to Kronig et al. on July 2, 1974 both disclose a process for the preparation of vinyl acetate catalysts comprising, And the solution A of the salt of gold and the compound solution B containing the compound solution B that can react with the described noble metal salt on the carrier to generate a water-insoluble metal compound are treated simultaneously or sequentially to the carrier, and such water-insoluble compounds are treated with a reducing agent to make converting a water-insoluble noble metal compound to a metal; washing the catalyst to remove water-soluble compounds; and coating an alkali metal compound, such as an alkali metal carboxylate, either before or after treatment with a reducing agent. Solution A may also optionally contain salts of several other metals, including copper salts.

US5332710 issued to Nicolau et al. on July 26, 1994 discloses a method for the preparation of a catalyst for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid, the method comprising impregnating a porous support; immobilization of palladium and gold as insoluble compounds on the support by soaking; inversion of the impregnated support in a reactive solution to precipitate such compounds; subsequent reduction of the compounds to their metallic forms.

US5347046 issued to white et al. on September 13, 1994 discloses a catalyst for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid, the method comprising preferably palladium group metals and/or their compounds, gold and/or their The compounds as well as copper, nickel, cobalt, iron, manganese, lead or silver or other compounds are deposited on the carrier material.

Summary of the invention

According to the present invention, there is provided a catalyst for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid, which has a low carbon dioxide selectivity, the catalyst comprising a porous carrier-on its porous surface deposited a catalytic Effective amounts of metallic palladium and gold - and copper acetate porous support. It is believed that the copper in the copper acetate allows the catalyst to achieve a lower carbon dioxide selectivity, which is often accompanied by a higher vinyl acetate production rate, than when copper acetate is not present in the catalyst. Detailed description of the invention

The carrier material in the catalyst of the present invention is made up of various regular shapes or irregular shapes, such as spheres, plates, cylinders, rings, stars or particles of other shapes, and its dimensions such as diameter, length Or a width of about 1 to about 10 mm, preferably about 3 to 9 mm. Spheroids with a diameter of about 4 to about 8 mm are preferred. The support material can consist of any suitable porous substance such as silica, alumina, silica-alumina, titania, zirconia, silicates, aluminosilicates, titanates, spinels, silicon carbide , charcoal, etc.

The surface area of the support material may be in this range, for example from about 10 to about 350 m2/g, preferably from about 100 to about 200 m2/g; its average pore size is in this range, for example from about 50 to about 2000 angstroms, And its pore volume is in this range, for example about 0.1 to 2 ml/g, preferably about 0.4 to about 1.2 ml/g.

In the preparation of the catalysts used in the process of the invention, the support material is first treated so that catalytic amounts of palladium and gold are deposited on the porous surface of the support material. Various methods can be used to achieve this. All of these methods involve simultaneous or separate impregnation of the support with an aqueous solution of one or more water-soluble palladium compounds and/or gold compounds. Examples of suitable water-soluble palladium compounds are palladium(II) chloride, palladium(II) chloride, palladium(II) potassium chloride, palladium(II) nitrate or palladium(II) sulfate, while gold(III) chloride ) or alkali metal salts of tetrachloroaurate(III) acid such as -sodium or -potassium salts can be used as water-soluble gold compounds. Alkali metal tetrachlorogold(III) acid and sodium palladium(II) chloride are preferred salts for impregnation because of their good water solubility. Impregnation can be accomplished by "incipient wetness" in which the amount of water-soluble metal compound solution used for impregnation is from about 95 to about 100% of the adsorption capacity of the support material. The concentration of the solution is such that the amount of the elements palladium and gold adsorbed on the support in the solution is equal to the desired predetermined amount. If more than one such impregnation is carried out, each impregnation may contain the water-soluble compound in an amount corresponding to the total amount or only a fraction of one or any combination of the two catalytically active metals desired in the final catalyst, as long as the adsorption The amount of these metals in the total impregnation solution is equal to the final desired amount. In particular, as described more fully below, it may be desirable to impregnate the support more than once with a solution of a water-soluble gold compound. The impregnation provides, for example, about 1 to about 10 grams of elemental palladium and, for example, about 0.5 to about 10 grams of elemental gold, the amount of gold being about 10 to about 125% by weight based on the weight of the palladium.

After each impregnation of the support with an aqueous solution of a water-soluble palladium salt and/or a water-soluble gold salt, by reacting in aqueous solution with a suitable basic compound such as an alkali metal hydroxide, silicate, carbonate or bicarbonate, The metal is "fixed", ie is precipitated as a water-insoluble compound such as a hydroxide. Sodium hydroxide and potassium hydroxide are preferred alkaline immobilizing compounds. The amount of alkali metal in the basic compound should, for example, be about 1 to about 2 times, preferably about 1.1 to about 1.8 times the amount required to react with the catalytically active cation in the water-soluble salt. The immobilization of the metal can be carried out by the incipient wetness method, wherein the impregnated support is dried, for example, at 150° C. for 1 hour, contacted with an amount of alkaline substance solution equal to about 95 to 100% of the pore volume of the support, and left to stand for about 0.5 to about 16 hours; or immobilization of the metal by the soaking method, wherein the undried impregnated support is soaked in a solution of an alkaline substance and rotated and/or turned at least during the initial stages of precipitation so that on the surface of the support particle Or a thin layer of precipitated water-soluble compounds forms near the surface. Spinning and tumbling can be performed, for example, at about 1 to about 10 rpm, for at least about 0.5 hour, preferably about 0.5 to about 4 hours. A contemplated spin-soak method is disclosed in US5332710, the entire disclosure of which is hereby incorporated by reference.

The catalyst containing the immobilized metal compound is first washed until it is free of anions such as halide ions, then dried, for example at 150°C for about 1 hour, and then the immobilized The, i.e. precipitated palladium compound and gold compound for 5 hours, or before washing and drying, such reduction is carried out in the liquid phase at room temperature with an aqueous solution of hydrazine hydrate, in which the hydrazine exceeds all that is present on the reduced support. The desired amount of metal compound ranges, for example, from about 8:1 to about 15:1, with reduction followed by washing and drying. Other reducing agents and methods for reducing the immobilized metal compound present on the support may be as conventionally used in the prior art. Reduction of the immobilized metal compound produces mainly the metal, although small amounts of metal oxides may also be present. In preparations with more than one impregnation and immobilization steps, the reduction can be carried out after each immobilization step or after all metal elements have been immobilized on the support.

As an example of the general procedure described above, the "split immobilization" method can be used to immobilize the catalytically active metal element on the support and to reduce the water insoluble metal compound to the desired metal form prior to impregnation with copper acetate. In this method, using the procedure specified above, the support is first impregnated with an aqueous solution of a water-soluble palladium compound by the incipient wetness method, and then by the incipient wetness method or the spin-soak method, preferably by the spin-soak method, by Sexual fixation is treated with a solution to immobilize palladium. The catalyst is then dried, impregnated alone with a solution of a soluble gold compound containing the desired amount of elemental gold in the catalyst, and then treated with an alkaline fixing solution by incipient wetness or spin-soaking, preferably incipient wetness. gold fixed. If gold is immobilized by incipient wetness, such immobilization can be combined with an impregnation step with a single aqueous solution of a soluble gold compound and a basic immobilizing compound in an amount greater than that which converts all of the gold in solution to The amount required to immobilize an insoluble gold compound such as gold hydroxide. If a hydrocarbon such as ethylene or hydrogen is used as the reducing agent in the gas phase, the catalyst containing the immobilized metal compound is first washed free of anions, dried, and reduced with ethylene or other hydrocarbon as described above. If hydrazine is used as the reducing agent in the liquid phase, the catalyst containing the immobilized metal compound is treated with an excess of hydrazine hydrate in water to reduce the metal compound to the metal before washing and drying as described catalyst.

Another specific method for the preparation of catalysts prior to impregnation with copper acetate is the "modified spin-soak" method, in which only a portion of the gold is impregnated with palladium during the first impregnation, using the spin-soak method, The metal is immobilized by reacting with a basic immobilizing compound, such as reducing the immobilized metal compound to a free metal with ethylene or hydrazine hydrate, washing and drying before ethylene reduction or after hydrazine hydrate reduction. The catalyst is then impregnated with the rest of the gold in the form of a solution of the water-soluble gold compound, and the catalyst is reduced again, for example with ethylene or hydrazine, after washing and drying, as described above, or before. This improved spin-soak method is more fully disclosed in WO94/08714, filed April 28, 1994, the entire disclosure of which is hereby incorporated by reference.

After preparing a catalyst comprising palladium and gold deposited in metallic form on a support material by any of the methods described above, the catalyst is then impregnated with an aqueous solution of monohydrated or anhydrous copper acetate, preferably by incipient wetness. The catalyst is then dried such that the finished catalyst contains, for example, copper acetate in an amount corresponding to about 0.3 to about 5.0, preferably about 0.5 to about 3.0 grams of elemental copper per liter of finished catalyst.

Advantageously, the catalyst containing palladium and gold in metallic form can also be impregnated with a solution of an alkali metal acetate, preferably potassium acetate or sodium acetate, more preferably potassium acetate. After drying, the finished catalyst may contain, for example, from about 10 to about 70, preferably from about 20 to about 60 grams of alkali metal acetate per liter of finished catalyst. When practiced, the optional impregnation of the catalyst with alkali metal acetate may be performed before or after the impregnation with copper acetate. However, it is preferred that the impregnation of alkali metal acetate is combined with the impregnation of copper acetate, that is, a catalyst containing metal palladium and gold is impregnated with a single solution of copper acetate and alkali metal acetate to obtain the desired content after drying. Quantities of the two acetates of the finished catalyst.

When the catalyst of this invention is used to prepare vinyl acetate, a gaseous stream containing ethylene, oxygen or air, acetic acid and the desired alkali metal acetate is passed over the catalyst. The composition of the gas flow can vary within wide limits, taking into account the explosion limits. For example, the molar ratio of ethylene to oxygen can be from about 80:20 to about 98:2; the molar ratio of acetic acid to ethylene can be from about 100:1 to about 1:100, preferably from about 10:1 to about 1:8; and The gaseous alkali metal acetate is present in an amount of from about 1 to about 100 ppm, based on the weight of acetic acid used. The gas stream may also contain other inert gases such as nitrogen, carbon dioxide and/or saturated hydrocarbons. Useful reaction temperatures are elevated temperatures, preferably about 150 to 220°C. The pressure employed may be slightly reduced, atmospheric or elevated, preferably up to about 20 atmospheres gauge.

An advantageous variant of the process for the production of vinyl acetate using the catalyst according to the invention is that the reactant feed stream to the process contains a halogen-free copper compound. The halogen-free copper compound is preferably sparingly soluble in water or acetic acid soluble, e.g. soluble at least about 0.3 g/l at 20°C, for example may be copper acetate (anhydrous or monohydrate) (copper acetate is preferred ), copper nitrate trihydrate or copper nitrate hexahydrate, copper sulfate (anhydrous or pentahydrate) or copper formate (anhydrous or pentahydrate), etc. The amount of copper compound fed to the reaction may, for example, be from about 10 ppb (parts per billion) to about 50 ppm (parts per million), preferably from about 20 ppb to about 10 ppm, of elemental copper relative to the acetic acid in the feed. By means of this characteristic, through the vaporization of the catalyst for a long time, the amount of copper in the copper acetate of the catalyst is reduced, so that the increase in carbon dioxide selectivity is reduced.

The following examples further illustrate the invention.

Example

In this example, a catalyst containing metallic palladium and gold on a support material was prepared by the "split immobilization" method, followed by impregnation with copper and potassium acetate.

The support consisted of Sud Chemie KA-160 silica pellets with a nominal diameter of 7 mm, a surface area of about 160 to 175 m2 ^/ g and a pore volume of about 0.68 ml/g, first using the incipient wetness method in an amount sufficient to obtain about The support material was impregnated with an aqueous sodium chloride palladium(II) solution of 7 g elemental palladium per liter of catalyst. Palladium was immobilized on the support as palladium(II) hydroxide by treating the catalyst with such an aqueous sodium hydroxide solution using the spin-soak method such that the Na/Cl molar ratio was about 1.2:1. The catalyst was then dried in a fluid bed drier at 100°C for 1 hour, followed by incipient wetness in an amount sufficient to obtain an aqueous solution of sodium tetrachloroaurate with 4 g of elemental gold per liter of catalyst and Na/Cl An aqueous sodium hydroxide solution with a molar ratio of about 1.8:1 impregnates the catalyst to immobilize the gold as gold hydroxide on the support. The catalyst was then washed with water until free of chlorides (approximately 5 hours) and dried at 150° C. for 1 hour in a nitrogen stream. Palladium hydroxide and gold hydroxide were then reduced to the metals by contacting the catalyst with ethylene (5% in nitrogen) at 150°C for 5 hours in the gas phase. Finally, by incipient wetness, the catalyst was impregnated with an aqueous solution of copper acetate monohydrate in an amount sufficient to obtain about 1.9 grams of elemental copper per liter of catalyst, and an aqueous solution of potassium acetate in an amount sufficient to obtain 40 grams of potassium acetate per liter of catalyst, followed by Dry in a bed dryer at 100-150°C for 1 hour.

The activity of the catalysts prepared as described in the examples in the production of vinyl acetate was tested by the reaction of ethylene, oxygen and acetic acid. For this test, approximately 60 ml of catalyst prepared as described was placed in a stainless steel wire basket and the temperature was measured with thermocouples on the top and bottom of the basket. The baskets were placed in a circulating Berty continuous stirred tank reactor and maintained at a temperature that would give approximately 45% oxygen conversion using a heating mantle. A gas mixture of about 130 liters/hour (measured at standard temperature and pressure) of ethylene, about 26 liters/hour of oxygen, about 128 liters/hour of nitrogen, about 131 grams/hour of acetic acid and about 2 mg/hour of potassium acetate at about 12 Pass through the basket at atmospheric pressure. The reaction was stopped after about 18 hours. Product analysis was performed by a combination of on-line gas chromatographic analysis and off-line liquid product analysis by condensing the product stream at about 10°C for optimal analysis of the final product. Such analysis showed a selectivity of 7.35% for CO2, a selectivity for heavy products of 0.98% and a relative activity of 1.70 expressed by the activity factor, which was calculated by computer as follows: The computer program used a series of activity factors Equations related to catalyst temperature (during the reaction), oxygen conversion, and a series of reaction kinetic parameters that occur during vinyl acetate synthesis. More generally, the activity factor is inversely proportional to the temperature required to achieve constant oxygen conversion.

The 7.35% _CO2 selectivity obtained in this example is significantly lower than that typically obtained with a similarly prepared 7 _mm palladium-gold catalyst without any copper acetate. A 7 mm palladium/gold catalyst without copper acetate prepared as described in Example 1 was found to have a _CO2 selectivity of about 9.3% and an activity of about 2.2.

Claims (18)

1. A method of preparing a catalyst for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid comprising impregnating a porous support containing catalytically effective amounts of metallic palladium and gold deposits with a solution of copper acetate. 2. The method according to claim 1, wherein said impregnating is carried out such that the copper acetate deposited on the impregnated catalyst contains from about 0.3 to about 5.0 grams of elemental copper per liter of catalyst. 3. The method of claim 2 wherein said copper acetate contains from about 0.5 to about 3.0 grams of elemental copper per liter of catalyst. 4. The method according to claim 1, wherein said porous support contains about 1 to about 10 grams of palladium per liter of catalyst and about 0.5 to about 10 grams of gold per liter of catalyst; About 125% by weight. 5. The method according to claim 1, wherein said copper acetate solution also contains dissolved alkali metal acetate. 6. The method according to claim 5, wherein said alkali metal acetate is potassium acetate deposited on the catalyst in an amount of from about 10 to about 70 grams per liter of catalyst. 7. A method according to claim 1, wherein said porous support containing catalytically effective amounts of metallic palladium and gold deposits is prepared by the steps of impregnating the porous support with an aqueous solution of a water-soluble palladium salt; by reacting with a suitable basic compound , immobilizing the palladium as a water-insoluble compound; subsequently impregnating the catalyst with a solution of a water-soluble gold salt; by reacting the dissolved water-soluble salt in such a solution with a suitable basic compound to precipitate the water-insoluble gold compound A method of immobilizing the gold present in the solution of the latter impregnation process; reducing the water-insoluble palladium compound and gold compound in the catalyst to their metallic state. 8. The method according to claim 1, wherein said porous support containing metallic palladium and gold deposits in a catalytically effective amount is prepared by the steps of using a water-soluble palladium salt containing all the desired elements of palladium on the finished catalyst and impregnation of the support with a solution of a water-soluble gold salt containing only a fraction of the amount of elemental gold desired on the finished catalyst; by rotating and/or inverting the impregnated support while soaking it in a solution of a suitable basic compound , to immobilize palladium and gold in the latter solution as water-insoluble compounds; to reduce the immobilized palladium and gold to their metallic states; to impregnate the catalyst with another amount of water-soluble gold salt solution so that the elemental gold in the catalyst total amount equal to the amount desired in the finished catalyst, said latter solution also containing a suitable basic compound sufficient to convert the supplementary gold to its water-insoluble compound so as to immobilize it in the desired quantity; to reduce the immobilized supplementary gold into its metallic state. 9. A method for producing vinyl acetate by reacting ethylene, oxygen and acetic acid as reactants, the method comprising, making said reactants with a porous carrier on which a catalytically effective amount of metal palladium and Gold- and copper acetate catalyst contacts. 10. 9. The method of claim 9, wherein said copper acetate is deposited on the catalyst in an amount of from about 0.3 to about 5.0 grams of elemental copper per liter of catalyst. 11. 10. The method of claim 10 wherein said copper acetate contains from about 0.5 to about 3.0 grams of elemental copper per liter of catalyst. 12. The method according to claim 10, wherein said catalyst contains from about 1 to about 10 grams of palladium per liter of catalyst, from about 0.5 to about 10 grams of gold per liter of catalyst; based on the weight of palladium, the amount of gold is from about 10 to about About 125% by weight. 13. The method according to claim 10, wherein said catalyst also contains deposits of alkali metal acetates. 14. The method according to claim 13, wherein an alkali metal acetate is fed into the reaction together with said reactants. 15. The method according to claim 14, wherein said alkali metal acetate is potassium acetate; the amount of potassium acetate fed into the reaction is from about 1 to about 100 ppm based on the weight of acetic acid used. 16. The method of claim 15 wherein copper acetate providing from about 10 ppb to about 50 ppm elemental copper, based on the weight of acetic acid, is fed to the reaction with said reactants. 17. A method according to claim 9, wherein a halogen-free copper compound is fed to the reaction together with said reactants. 18. The method according to claim 17, wherein said halogen-free copper compound is copper acetate.